I live in Eretz Yisroel, and I am sure the Rov is familiar with our timers. It is the type that the trippers do not separate from the clock at all, but just get moved from an on/ off position I set the air-conditioner timer before Shabbos. On Shabbos morning, I realize I set it to go on too early. It is not on yet; it’s 2 hours away from turning on. Can I click, in a k’lacher yad way, the red notch thing on the timer to go on a bit later, without interfering at all with any electricity of the timer itself?
It is controversial if this is permitted, R’ S. Z. Auerbach permits moving the trippers of a Shabbos clock if it is going to keep the present situation longer but not if it will shorten it. For example he says that one may move the trippers to keep a light on longer, but not to turn it off quicker. Most other poskim however don’t allow it, for two reasons, muktza and because moving the trippers is considered doing a direct action of turning it on and not merely a grama.
From a practical standpoint, aside from the fact that most poskim prohibit it, from a practical angle it is not advisable for you to do this. This is because very often people make mistakes, between elongating the present situation and shortening it. Additionally there are times when the dial etc. gets moved by mistake and the person ends up actually turning the light on or off. Even R’ S. Z. is quoted as saying that this idea should not be used unless there is a strong need for it, such as to help a sick person.
Igros Moshe O:CH 4-91(5), Shvus Yitzchok 6 pg. 149, Beer Moshe 6 – Kuntris Electric 36, Mishne Halachos 8-35, Oz nidberu, 3-25, Btzel Hachochma 2-32, Yaskil Avdei 4-17, R’ Vosner quoted in Meohr HaShabbos 4- chap. 14 ftnt. 237, R’ C. Kanievsky quoted in Nezer Hachayim pg. 189, Minchas Shlomo 2- 23, Orchos Shabbos 29-9 footnote 26, 29.